Preparation, characterization and reaction performance of H-ZSM-5/cobalt/silica capsule catalysts with different sizes for direct synthesis of isoparaffins
Preparation, characterization and reaction performance of H-ZSM-5/cobalt/silica capsule catalysts with different sizes for direct synthesis of isoparaffins
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DOI：
10.1016/j.apcata.2007.06.028
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发表时间：
2007-10
影响因子：
5.5
通讯作者：
Guohui Yang;JingJiang He;Y. Yoneyama;Yisheng Tan;Yizhuo Han;N. Tsubaki
中科院分区：
文献类型：
--
作者：
Guohui Yang;JingJiang He;Y. Yoneyama;Yisheng Tan;Yizhuo Han;N. Tsubaki
采用直接水热合成法，将直接合成的H-ZSM-5分子筛膜完美包覆在不同粒径的Co/SiO2催化剂颗粒上，制备了3种H-ZSM-5分子筛胶囊催化剂。采用SEM、EDS和XRD等手段对催化剂的形貌进行了表征，并对沸石胶囊的H-ZSM-5结构进行了鉴定。采用NH3-TPD和气体吸附法对催化剂的表面酸性和孔结构进行了表征。结果表明，在相同的合成条件下，粒径较小、外表面较大的Co/SiO2颗粒有利于沸石胶囊的生长。分别使用常规费托合成（FTS）催化剂Co/SiO2、Co/SiO2与H-ZSM-5的物理混合催化剂以及沸石胶囊催化剂进行FTS反应。在胶囊型催化剂和混合型催化剂上均能选择性地得到异构烷烃。由于空间限制效应和择形效应，胶囊催化剂比混合催化剂具有更高的异链烷烃选择性。特别是小粒径的胶囊催化剂具有更高的CO转化率和异构烷烃选择性。通过改变载体颗粒的大小可以控制胶囊催化剂的结构、活性和选择性。
Three kinds of H-ZSM-5 zeolite capsule catalysts were prepared by a direct hydrothermal synthesis method, where directly synthesized H-ZSM-5 membrane was coated perfectly onto Co/SiO2catalyst pellets of different sizes. SEM, EDS and XRD were used to characterize the catalyst morphology and to identify the H-ZSM-5 structure of zeolite capsules. Surface acidity and pore property of these catalysts were tested by NH3-TPD and gas adsorption. The results showed that smaller Co/SiO2pellets with large external surfaces were favorable for zeolite capsule growth under the same synthesis conditions. The Fischer–Tropsch synthesis (FTS) reactions using the conventional FTS catalyst Co/SiO2or the physically mixed catalyst of Co/SiO2with H-ZSM-5, or the zeolite capsule catalysts were each conducted. The isoparaffins were selectively obtained on the capsule catalysts and the mixed catalyst. The capsule catalysts exhibited higher selectivity of isoparaffins than the mixed catalyst due to the space-confined effect and the shape-selective effect. Especially, capsule catalysts with smaller sizes showed higher CO conversion and higher isoparaffin selectivity. Changing the substrate pellet size could control the capsule catalysts’ structure and their activity as well as their selectivity.